1.1 Field of the Invention
The present invention relates generally to the fields of molecular biology. More particularly, certain embodiments concern methods and compositions comprising DNA segments, and proteins derived from bacterial species. More particularly, it concerns a novel cryET29 gene from Bacillus thuringiensis encoding a coleopteran- and cat flea-toxic crystal protein. Various methods for making and using these DNA segments, DNA segments encoding synthetically-modified CryET29 proteins, and native and synthetic crystal proteins are disclosed, such as, for example, the use of DNA segments as diagnostic probes and templates for protein production, and the use of proteins, fusion protein carriers and peptides in various immunological and diagnostic applications. Also disclosed are methods of making and using nucleic acid segments in the development of transgenic plant cells containing the DNA segments disclosed herein.
1.2 Description of the Related Art
1.2.1 Bacillus thuringiensis Crystal Proteins
Bacillus thuringiensis is a Gram-positive bacterium that produces .delta.-endotoxins known as crystal proteins which are specifically toxic to certain orders and species of insects. Many different strains of B. thuringiensis have been shown to produce insecticidal crystal proteins. Compositions including B. thuringiensis strains which produce insecticidal proteins have been commercially available and used as environmentally acceptable insecticides because they are quite toxic to the specific target insect, but are harmless to plants and other non-targeted organisms.
The B. thuringiensis crystal protein is toxic in the insect only after ingestion when the alkaline pH and proteolytic enzymes in the insect mid-gut solubilize the crystal protein and release the toxic components. These components disrupt the mid-gut cells causing the insect to cease feeding and, eventually to die. In fact, B. thuringiensis has proven to be an effective and environmentally safe insecticide in dealing with various insect pests.
As noted by Hofte et al., (1989) the majority of insecticidal B. thuringiensis strains are active against insect of the order Lepidoptera, i.e., caterpillar insects. Other B. thuringiensis strains are insecticidally active against insects of the order Diptera, i.e., flies and mosquitoes, or against both lepidopteran and dipteran insects. In recent years, a few B. thuringiensis strains have been reported as producing crystal proteins that are toxic to insects of the order Coleoptera, i.e., beetles. To date, there have been no reports of B. thuringiensis strains active on fleas of the Genus, Ctenocephalides, in the order Siphonaptera.
The dipteran-active Cyt toxins differ from most of the other B. thuringiensis insecticidal crystal proteins in that they are smaller and do not share conserved blocks of sequence homology. These proteins demonstrate broad cytolytic activity in vitro, yet are specifically toxic to larvae of dipteran insects in vivo. These properties have been described elsewhere (Chilcott and Ellar, 1988).
1.2.2 Genetics of Crystal Proteins
A number of genes encoding crystal proteins have been cloned from several strains of B. thuringiensis. The review by Hofte et al. (1989) discusses the genes and proteins that were identified in B. thuringiensis prior to 1990, and sets forth the nomenclature and classification scheme which has traditionally been applied to B. thuritigiensis genes and proteins. cryI genes encode lepidopteran-toxic CryI proteins. cryII genes encode CryII proteins that are toxic to both lepidopterans and dipterans. cryIII genes encode coleopteran-toxic CryII proteins, while cryIV genes encode dipterantoxic CryIV proteins.
Recently a new nomenclature has been proposed which systematically classifies the cry genes based upon DNA sequence homology rather than upon insect specificities. This classification scheme is shown in Table 1.
TABLE 1 ______________________________________ Revised B. thuringiensis .delta.-Endotoxin Gene Nomenclature.sup.a New Old GenBank Accession # ______________________________________ Cry1Aa CryIA(a) M11250 Cry1Ab CryIA(b) M13898 Cry1Ac CryIA(c) M11068 Cry1Ad CryIA(d) M73250 Cry1Ae CryIA(e) M65252 Cry1Ba CryIB X06711 Cry1Bb ET5 L32020 Cry1Bc PEG5 Z46442 Cry1Ca CryIC X07518 Cry1Cb CryIC(b) M97880 Cry1Da CryID X54160 Cry1Db PrtB Z22511 Cry1Ea CryIE X53985 Cry1Eb CryIE(b) M73253 Cry1Fa CryIF M63897 Cry1Fb PrtD Z22512 Cry1G PrtA Z22510 Cry1H PrtC Z22513 Cry1Hb U35780 Cry1Ia CryV X62821 Cry1Ib CryV U07642 Cry1Ja ET4 L32019 Cry1Jb ET1 U31527 Cry1K U28801 Cry2Aa CryIIA M31738 Cry2Ab CryIIB M23724 Cry2Ac CryIIC X57252 Cry3A CryIIIA M22472 Cry3Ba CryIIIB X17123 Cry3Bb CryIIIB2 M89794 Cry3C CryIIID X59797 Cry4A CryIVA Y00423 Cry4B CryIVB X07423 Cry5Aa CryVA(a) L07025 Cry5Ab CryVA(b) L07026 Cry5B U19725 Cry6A CryVIA L07022 Cry6B CryVIB L07024 Cry7Aa CryIIIC M64478 Cry7Ab CryIIICb U04367 Cry8A CryIIIE U04364 Cry8B CryIIIG U04365 Cry8C CryIIIF U04366 Cry9A CryIG X58120 Cry9B CryIX X75019 Cry9C CryIH Z37527 Cry10A CryIVC M12662 Cry11A CryIVD M31737 Cry11B Jeg80 X86902 Cry12A CryVB L07027 Cry13A CryVC L07023 Cry14A CryVD U13955 Cry15A 34kDa M76442 Cry16A cbm71 X94146 Cyt1A CytA X03182 Cyt2A CytB Z14147 To Be Assigned CryET29, Present Invention To Be Assigned ______________________________________ .sup.a Adapted from: http://www.susx.ac.uk:80/users/bafn6/bt/index.html
1.2.3 Identification of Crystal Proteins Toxic To Coleopteran Insects
The cloning and expression of a gene encoding a 26-kDa mosquitocidal toxin from the dipteran-active B. thuringiensis var. israelensis has been described (Ward et al., 1984), and the nucleotide sequence of this gene was reported (Ward and Ellar, 1986). The molecular mass of the toxin protein, CytA, calculated from the deduced amino acid sequence was determined to be 27,340 Da.
The nucleotide sequence of the gene for a 27-kDa mosquitocidal Cyt protein isolated from B. thuringiensis var. morrisoni strain PG14 has been disclosed (Earp and Ellar, 1987). The sequence of this toxin protein was found to differ by only one amino acid residue from the CytIA protein of B. thuringiensis var. israelensis.
The identification of a 25-kDa protein that exhibits cytolytic activity in vitro when activated by proteolysis from the mosquitocidal B. thuringiensis var. kyushuensis was described earlier (Knowles et al., 1992), and the nucleotide sequence of the gene for this protein, CytB, was reported (Koni and Ellar, 1993). The predicted molecular mass of the CytB protein is 29,236 Da and the deduced amino acid sequence is quite distinct, although it does share significant sequence similarity with the CytA protein of B. thuringiensis var. israelensis.
The cloning and characterization of the gene for a 30-kDa toxin protein with activity on coleopteran and dipteran insects has been described (Intl. Pat. Appl. Pub. No. WO 95/02693, 1995). This gene, isolated from B. thuringiensis PS201T6, encodes a protein of 29,906 Da which exhibits a 64% sequence identity with the CytA toxin of B. thuringiensis var. israelensis.